lockstat: Fix construction of comparision predicates

Passing "0x%p" to sprintf results in double "0x" being printed.
This causes a dtrace script compilation failure when "-d" flag
is specified.
Fix that by removing the extraneous "0x".

Reviewed by: markj
Approved by: mw(mentor)
Obtained from: Semihalf
Sponsored by: Alstom
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D35690